Interpretations are issued to explain and clarify the intent of a standard and do not constitute an alteration to the original standard. In addition, interpretations are not intended to supply consulting information. Permission is hereby granted to download and print one copy of this document. Individuals seeking permission to reproduce and/or distribute this document in its entirety or portions of this document must contact the IEEE Standards Department for the appropriate license. Use of the information contained in this document is at your own risk.

I would like to request a formal interpretation on the following
issue concerning the mailx utility in POSIX.2.
In subclause 4.40.7, the Extended Description of the mailx
command, (P342, L6312-6321), it says:
... When mailx is invoked using the Send Mode synopsis, and
standard input is a terminal, if no subject is
specified on the command line and the asksub variable is set, a
prompt for the subject shall be written.

At
this point mailx is in input mode. This input mode is also entered
when using one of the Receive Mode
synopsis forms and a reply or new message is composed using
reply, Reply, or mail commands. When the
message is typed and the end of the message is encountered,
the message shall be passed to the mail
delivery software. Commands can be entered by beginning a line
with the escape character [by default,
tilde (~)] followed by a single command letter and optional
arguments....
Does the definition of "input mode", then, necessarily require
that stdin is a terminal? This seems unclear
when Receive Mode is involved. That is to say, does
echo "reply 1\naaaa\n~w repl" | mailx -n -f mbox
produce a mail message sent to the all recipients of the first
message in mbox which contains the message
aaaa
~w repl
or does it mail a message containing
aaaa
and create a copy of this message in the file repl?

To match historic practice of the System V mailx, on which the
standard is based, the sentence on P342,
L6315-6317, should be changed to:
This input mode is also entered when using one of the Receive
Mode synopsis forms and a reply or new
message is composed using the reply, Reply, or mail commands,
and stdin is a terminal.
Also, a sentence needs to be added after the end of the
paragraph ending on (P342, L6321) which
states:
It is unspecified what effect these commands will have if stdin is
not a terminal when a message is entered
using either the Send Mode synopsis, or the Read Mode
commands reply, Reply or mail.
I believe that this change to historic practice was not intended.
The rationale for mailx seems to carefully
point out the cases where the standard differs from historic
practice, but does not mention this issue.

Interpretation Response #102
The standard clearly states the behavior of "input mode" and
stdin, and conforming implementations must
conform to this. However, concerns have been raised about this
which are being referred to the sponsor.